(rant start)
Thanks a lot to people that tell Flash to go die. Now we couldn't even stop auto buffer/download.
.(rant end) :laughing:

And no browsers interest in develop it. Obviously, don't ask Chromium or Google about it.
All was depended & left to web author mercy. They need to also set up auto play & auto buffer properties. W3C standard.

For Auto play, extension does available.Disable HTML5 Autoplay.
This the only one available & work, kudos to the author.

The only way worthy enough, is by blocking HTML5 video/audio property completely. Like using HTML Content Blocker. Its "Media" option will block HTML5 multimedia. Unfortunatelly, still no whitelist/blacklist. It's a take it or leave it.